1. Field of the Invention
This invention relates generally to methods for cleaning inner surfaces of containers of indirect extrusion presses, and more particularly to a method for cleaning inner surfaces of a container by utilizing an extruding die itself, permitting continued use of the die after contributing to the cleaning in each cycle of press operation to ensure uniform accuracy of extruded products. It is also contemplated to shorten the time period of the cycle of the press operation. The method provides especially good results in the production on a small scale of diversified kinds of extruded articles.
2. Description of the Prior Art
In the production of various extruded articles of high tensile aluminum alloys for indirect extrusion presses, it is generally required to remove shells deposited on the inner surfaces of a container prior to the extruding phase in each cycle of operation in order to have good surface quality of the product. In this regard, there have been employed various cleaning mechanisms, including cleaning edges or edged surfaces formed on a die to clean the container by the die itself, use of a dummy block or resort to mechanism which is exclusively provided for cleaning. From the viewpoint of shortening the press cycle time, the method of utilizing a die itself is advantageous as cleaning is effected simultaneously with extrusion. However, the provision of an edged surface or edges integrally on the extruding die in turn gives rise to the necessity of removing the shells which have been transferred onto the die, in addition to the problem of abrasive wear of edged surfaces or cleaning edges. Since it is difficult to remove the shells from the die during the dry cycle time of the press, the conventional procedure has been to provide a plurality of dies, using one die in each cycle of extruding operation while removing shells from other dies at a point outside the press machine. Therefore, it has been necessary to provide more than two dies of exactly the same design, which is obviously disadvantageous in view of the die cost as well as the severe tolerance of errors as imposed in the die manufacture, and from which no further reductions of the time period of the cycle of the press operation can be expected. The preparation of dies of uniform dimensions is extremely difficult, especially in the situation of extrusion of products having a thin profile. Therefore, application of the above-mentioned method is limited to extruding operations of the sort which involves drawing in a subsequent stage. The cleaning of the container by the extruding dies requires higher die costs on a small-scale of diversified kinds of extrusion articles.